Amplifying device



Oct. 7, 1947. A. B. sMlrH 2,428,687

AMPLIFYING DEVICE Filed Aug. 20, 1943 FIG, 2 5

lo @ladle1t lab b kk QCM/b5 24 l2c E@ 23 n@ i9 Il l 180 loalcz 188mb 33 O. N N Mz'LLlc 3 u 3; 5 AND 10N MAeNeTu:` 34h I8 Se "a FIG@ INVENTOR. yARTHUR BESSEY SMITH ATTORNEYS Patented Oct. 7, 1947 AMPLIFYING DEVICE Arthur Bessey Smith, Evanston, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application August 2.0, 1943, Serial No. 499,357

7 Claims.

This invention relates to improvements in amplifying devices and its purpose is to provide an improved electrically operated mechanical amplier of audible frequencies adapted for use in telephone systems, loud speaker systems and the like where it is desirable to amplify the vibrations produced by telephone speech.

In a device of this' type, an armature is mounted to vibrate between the pole faces of a polarized electromagnet and is operatively connected to the electrodes of microphone cells. The alternating current to be amplified energizes the coils of the electromagnet and vibrates the armature, thereby actuating the electrodes of the microphone cells and producing undulations in a connected direct current circuit which includes an induction coil or transformer for sending out oscillations of increased power or amplitude.

In an amplifier of this type, as heretofore generally constructed, the armature, which is ordinarily pivotally mounted, is in unstable equilibrium in its central or neutral position and tends to snap powerfully to either extreme position due to the action of the polarized magnet. For a limited movement in either direction from this neutral position, the armature is attracted by a magnetic force which is linean that is, it increases in a uniform manner as the pole faces are approached,rbut as the end portions of the armature approach very closely to the pole faces the magnetic force increases very rapidly, thus producing irregularity and instability in armature action.

The principal object of the present invention is to overcome the above-mentioned difficulties, in an improved manner, by providing an amplifying device of the type referred to in which the magnetic torque due to the polarization of the magnetizable core is substantially neutralized so that the armature tends to remain in any position to which it is moved and is thus in a stable position at all times within its field of vibration. This is preferably accomplished by the use of a spring or other equivalent device which opposes the movement of the armature from its central or neutral position and which tends to return it to that position. By this means, the present invention tends to prevent any tuning of the vibrations of the armature for any particular frequency in the receiving circuit and insures the desired uniformity of operation.

An important feature of the invention is the provision in an amplifier of the type referred to of means for confining the vibrations of the armature substantially to the range in whichI lh@ magnetic attraction increases uniformly as the pole faces are approached. This object may preferably be attained by providing the pole faces with coatings of non-metallic material such as paper, yarn or the like which may be applied in any desired thickness and which not only conne the armature to the desired range of movement during its normal operation but also prevent the sticking of the armature to the pole faces when starting. f

A further object is to provide an improved mlcrophone cell which may be used in an amplifier circuit or other circuit for setting up oscillations in response tomovements of a connected vibrating armature or the like. In its preferred form this microphone cell comprises a chamber containing carbon granules and connected with the armature or other actuating member by a flexible non-metallic member, which may be a tubular collapsible member forming a continuation of said chamber and'containing some of said carbon granules which are held thereby in contact with the actuating member. The armature or other actuating member is preferably provided with a non-magnetic contact plate which directly engages the carbon granules and this contact plate and the interior surfaces of said chamber are preferably plated with gold or the like to improve the microphonic action.

These and other objects of the invention will be more fully understood from the following speciiication taken with the accompanying drawings in which one embodiment is illustrated. In the drawings,

Figure 1 shows a side elevation of one form of the improved amplifier of the present invention;

Fig, 2 shows a horizontal section through the improved amplifier of the present invention, the section being taken on .the line 2-2 of Fig. 1;

Fig, 3 is a diagram showing the balancing effect of the polarized magnet and the resilient mounting of the armature within the working range of movement of the armature;

Fig. 4 shows an end elevation of the structure illustrated in Fig, 1, looking toward the left as viewed in Fig. l;

Fig. 5 shows a perspective view of the front half of the winding shell or spool, which is embodied in the structure illustrated in Figs. 1 and 2, with' the armature mounted therein;

Fig. 6 shows a transverse section taken on the line 6 6 of Fig. 5, showing the manner in which the armature is held in position in the spool; and

Fig. 7 is a circuit diagram illustrating one set Y of circuit connections which may be employed in using the amplier illustrated in Figs. 1, 2 and 4.

As illustrated in the drawings, the improved amplifier comprises a U-shaped permanent magnet I formed of steel which has its parallel arms IIla and IDb, as viewed in Fig. 2, connected to a pair of U-shaped pole pieces II and I2, respectively, interposed between them and formed of magnetizable material such as soft iron. The pole piece comprises a pair of eld members or side plates IIa and IIb terminating in pole faces ||c which are opposed to the pole faces I2c formed on the field members or side plates |28 and |211, respectively, of the opposite pole piece. A pair of plates I3, formed of a phenol condensation product or other hard insulating material, engage the outer sides of the front and rear arms Ie and Il!b of the magnet Il!l and project beyond the upper and lower edges of these arms. These plates are secured togeth'er by bolts I4 which have their threaded extremities engaged by nuts I5. The front and rear arms of the magnet IIJ are adapted to be drawn together by tightening the nuts I5 for the purpose of regulating the spaced relationship of the pole faces IIc and I2C and to clamp together the two parts of the winding spool hereinafter described. The extent to which' the arms of the magnet I0 may be thus drawn together is limited by the spacing sleeves I6 which extend between the plates I3 and are engaged by the bolts I4.

The chamber formed by the opposed U-shaped pole pieces and I2 is occupied by a winding spool I8 which is made up of a front half I8a and a rear upper half |8b, both formed of molded insulating material, such as Bakelite. The spool I8 has a central passage I9 in which there is mounted the armature 20 which is formed as a flat plate made of magnetizable material such as soft iron. The construction of the spool I8 and the method of mounting the armature 2D therein are illustrated in the United States Letters Patent of Albert Earl Woodruff and Albert Frederick Horlacher, No. 2,241,105, dated May 6, 1941. The hub of the winding spool comprises a front plate I8c and a rear plate |8fl which are united at their ends with outwardly extending plates or flanges I8e and I8f, respectively. These plates I8e and I8f t within the side plates IIb and |211, respectively, of the pole pieces II and I2 and they are adapted to have wound around them the insulated wire forming the magnetizing coil 2| which is adapted to be connected in the input circuit over which is received the alternating current of audible frequency to be amplified and in response to which th'e armature 2D is vibrated.

The front half I8a of the winding spool I8 is shown particularly in Figs. 5 and 6 Where it is illustrated as comprising the plate I8c and the flanges |88, previously referred to, with the plate I8c cut away longitudinally on its inner side to form a groove or recess I8g in which is mounted the body portion of the armature 20 having the form of a rectangular plate. As shown in Fig. 6, th'e rear half I8b of the spool has its central plate I8d cut away in a similar manner to form a groove or recess I3h and the two recesses I Ilg and I8h thus form a chamber in which the intermediate portion of the armature 20 is free to move when the end portions thereof vibrate between the opposite pole faces of the pole pieces II and I2, the faces of the grooves or recesses I8g and I 8h being substantially flush with the pole faces IIc and I2C, respectively, when th'e parts are assembled as shown in Fig. 2.

At the sides of the recess I8?, the center plate I8c of the front half of the spool is provided with outwardly extending notches I8x which communicate with enlarged notches II!j extending inwardly from the outer lateral edges of the part ISC. The openings I81 are adapted to receive and be loosely engaged by outwardly projecting trunnions 2|)a which' are integrally formed on the armature 20 at its opposite sides and midway between its ends. These trunnions are formed integrally with enlargements 2l!b in the form of rectangular heads which t tightly within the notches |81', as shown at the lower side of Fig. 5. After these trunnions 2l)a and the head 2|)b have been put in place, spring metal clips 22 are placed aroundv the lateral edges of th'e center plate IISc of the front part of the spool with the flanges 22e thereof overlying the heads 20h of the armature, as shown in the upper part of Fig. 5, and with their other flanges 22b underlying the center plate I8c of the spool. These parts 22 very rmly clamp the armature trunnion h'eads ZI'Jb so that they are securely retained in place and cannot move. The vibration of the armature twists the trunnions 20a which have sumcient resilience for the purpose. When the parts are thus assembled, as shown in Fig. 6, the edges of the ilanges llie and I8f which are formed on the front and rear halves of the spool, respectively, engage each other along surfaces 20k, thus limiting the extent to which the two halves of the spool may be forced together by the clamping action exerted through the tightening of the nuts I5 on the bolts I4. In this way, a rigid assembly is brought about withl the pole pieces and the parts of the spool securely clamped in place between the upper and lower arms of the magnet I0 while at the same time providing a chamber in which the armature 20 is free to vibrate under the iniluence of the magnetic forces set up through the action of the alternating current passing through the coil 2|.

The magnetizable material of which the armature 25 is formed should be somewhat resilient so that the armature will be capable of vibration through the twisting of the trunnions 2|)a which connect the body of the armatureV with the xed integrally formed heads 20h. Upon a tilting movement of the armature in either direction from its neutral position, the trunnions 20a will be put under torsional stress and be twisted so that they will act as springs which tend to return the armature to its neutral position midway between the pole faces, as illustrated in Fig. 2. By suitably proportioning the dimensions of the trunnions 20a, this spring action may be caused substantially to neutralize the polarizing effect of the permanent magnet I0, within the normal range of the vibratory movement of the armature 20, so that the armature will occupy a floating position between the pole pieces and will tend to remain in any position to which it is moved except as it is influenced by the magnetizing forces set up by the current passing through the coil 2| This balancing effect of the spring action of the trunnions 2|!a and the neld of the permanent magnet, throughout the normal working range of movement of the armature, is illustrated diagrammatically in Fig. 3 where the abscissa minus X and plus X represent linear movements of the armature ends from a neutral or intermediate position between the pole faces and where the ordinate plus T and minus T represent the torque exerted on the armature. The point I) represents the neutral or central position of the armature and the force exerted on the armature by the permanent magnet |0 as the armature moves from that central position is shown by the vcurve M. The force exerted by the spring action of the trunnions 2lia in various positions of the armature is shown by the straight line S. It will be observed that the curve M is a straight line within a range of movement of the armature between the lines plus F and minus F, indicating a. linear variation of the magnetic force according to the distance of the armature from the neutral position, whereas the magnetic force increases very rapidly and at an increasing rate when the armature moves beyond the range indicated by the lines plus F and minus F to positions closer to the pole faces, as shown by the curved extremities of the curve M. Thus, by confining the movement of the armature to the working range indicated by the distance between the lines plus F and minus F, it is possible, by a suitable proportioning of the parts, to cause the spring action of the trunnions substantially to neutralize the magnetic torque dueto the polarization of the permanent magnet I0 in al1 positions of the armature within this range, so that the armature will remain in any of these positions to which it is moved, when the magnetizing coil 2| is not energized.

In order to confine the movement of the armature within the linear range just referred to wherein the magnetic forces exerted through the pole pieces by the permanent magnet ||l will vary uniformly with changes in the position of the armature, as heretofore described, and to prevent the armature from adhering to the pole faces, the pole faces |c and |2c are provided with coat ings 23 of non-metallic and non-magnetic material such as paper, yarn or the like which may be cemented or otherwise secured to the pole faces and which may have any desired thickness adapted to coniine the movements of the armature within the prescribed range.

The amplifying device should be so mounted that the armature 20 will be located in a vertical plane and this armature is provided at one end with a projecting ear 2|)c having an aperture 2|)li therethrough to receive a short bolt 24 which secures in place a U-shaped brass clip or contact plate 25, thearms of which embrace the ear 20c. A nut 26 engages the bolt 24 to secure the clip 25 in place and this clip serves as a non-magnetic contact member for actuating the microphone cells 3|) which are disposed on opposite sides thereof Without extending the ear 20C and une balancing the armature, The cells are arranged with their axes extending horizontally and they are carried by a pair of insulating blocks 3|, formed preferably of Bakelite, which are secured to the upper and lower plates |3 by screws 32.

Each cell 30 comprises a metal tube 33 formed of brass or other non-magnetizable metal and having a press t in a vertical hole 3| i formed in one of the blocks 3|. These tubes are internally threaded at their outer ends and these ends are closed by threaded plugs 34. Large washers 34*L are placed over the ends of 4the tubes 33 and are secured in place by terminal screws 34b entering threaded holes in the outer ends of the plugs 34 and providing means for making connections with an electricycircuit. rI'he tubes 33 project from the blocks 3| toward the contact plate 25 but terminate short of it to a substantial degree so that the plate may move freely between the ends of the tubes. The projecting end of each tube is fitted by a exilble sleeve formed of loosely woven silk cloth. Each cloth sleeve 35 is spread out at its base to form a ilange 35a seating against the adjacent 'block 3| and it extends beyond its tube 33 to the face of the contact plate 25 where it is again spread out to form another annularflange 35b seating against this plate. There is thus formed on each side of the contact plate of the armature a cell chamber 36 made up partly of the lbore of a tube 33 and partly of the lcloth sleeve and each of these chambers is sulbstantially lled with a quantity of carbon granules 31. To improve the microphonic action of the cells, the metallic parts engaged by the carbon granules, including the contacting surfaces of the plate 25, the internal surfaces of the tubes 33 and the ends of the plugs 34, are preferably gold plated. The car-bon granules are adapted to be compressed on one side of the armature contact plate 25, upon movement of the armature, at the same time that the pressure on the granules at the other side of the contact !plate is reduced, thus producing a differential action in the circuit of Fig. '7 in which the cells 30 are connected.r As vibration of the armature takes place, the exible cloth sleeves 35 which form the inner ends of the icell chambers readily adjust themselves to the changing position of the vcontact plate 25. The initial compression of the carbon granules 31 in these cells may be regulated by adjusting the positions of the threaded plugs 34 inthe tubes 33. y

One method of using the improved amplifier is diagrammatically shown in Fig. '7 which illustrates the magnetizing coil 2| as` lbeing connected in an alternating current telephone input circuit 40 over which is received the current of audible frequency to be amplified. Assuming that the arm r.Illb is the north pole of thepermanent magnet I0, the magnetic field produced in the armature by the alternations. of the current in the input circuit acts rst to supplement the fiux passing from onepositive pole piece I2a and then to supplement that from the other positive pole |211, so that the positive poles alternately exert greater attractive forces on the opposite armature ends, thus causing the armature to vibrate about the axis of the trunnions 23a. During this action, the magnetic iiux produced by the current in the coil 2| is, at a given instant, added to a part of that passing from one pole piece |22 into the armature and this flux passing through the armature enters the negative pole piece |b at the other end of the armature; upon reversal of the current in the coil 2|, the direction of the iield in the armature is reversed and its flux is then added to a part of that passing from the other pole piece |2b, thus producing a pulsating magnetic field acting on the ends of the armature.

These vibrations of the armature are imparted to the microphone cells 30 which are differentially connected in the direct current circuit 4|, as shown in Fig. 7. This circuit includes conductors 42, connecting the terminals of the cells 30 to the terminals of the primary winding of an induction coil 43, and a conductor 44 connected to the contact plate 25 between the two cells and leading through a battery 45 to the middle point of the primary winding. The secondary winding of the induction coil 43 is connected to the output circuit 46.

The vibration of the armature 2|) actuates the two microphone cells. 30 differentially, one rising in resistance as the other falls, and vice versa. The currents in the two parallel conductors 42 tend to neutralize each other in the induction coil and the magnetism in the core of the coil is due to the difference in the ampere-turns of the two sections of the primary winding of the coil which are connected to these two conductors 42. As the resistance of one microphone cell decreases and its current increases, the resistance of the other microphone cell increases and its current decreases and, since the two parts of the primary winding have the same number of turns, the vibration of the armature causes an alternating magnetism in the core and an alternating voltage in the secondary winding of the induction coil which is connected in the output circuit 46. The output current has the same wave shape as the input current but is very much stronger, thus producing the desired amplification of the input current and making it possible to obtain the desired strength of reproduction of the speech or other sounds transmitted, through the use at the receiving end of the circuit of a suitable sound translating device.

Although one form of the invention has been shown and described by way of illustration, it will be understood that it may be constructed in vario-us other embodiments which come within the scope of the appended claims.

Iclaim:

1. In an amplifying device, a polarizing magnet, field members of magnetizable material connected to said magnet and having opposite pole faces spaced apart, means for varying the spaced relation of said pole faces, an armature mounted for movement between said pole faces, means secured to said pole faces for confining the vibrations of said armature to a range in which the magnetic attraction thereon varies uniformly with the variation in the distance of the armature from the attracting pole face, means for balancing the magnetic force exerted on said armature by said magnet in different positions of said amnature, and means for setting up a pulsating magnetic field in said field members for actuating said armature.

2. In an amplifying device, a polarizing magnet, field members of magnetizable material connected to said magnet and having opposite pole faces spaced apart, an armature mounted for movement between said pole faces, means applied to said pole faces for confining the movement of said armature within a predetermined range in which the magnetic attraction thereon varies uniformly with the variation in the distance of the armature from the attracting pole face, means for balancing the magnetic force exerted on said armature by said magnet in all positions of said armature within said range, and means for setting up a pulsating magnetic field in said field members thereby to actuate said armature.

3. In an amplifying device, a polarizing magnet, field members formed of magnetizable material connected to the opposite end portions of said magnet and having opposed pole faces spaced apart, an armature mounted for movement between said pole faces, resilient means providing the sole support for said armature and acting normally to balance the attractive force of said magnet, a winding adapted to be connected in an alternating current circuit and arranged to set up a pulsating magnetic field in said field members to cause said armature to vibrate between said pole faces, a microphone cell arranged to be actuated by the movement of said armature, and means for confining the vibrations of said armature to a range in which the magnetic attraction thereon varies uniformly with the variation in the distance of the armature from the attracting pole face,

4. In an amplifying device, a polarizing magnet, field members of magnetizable material connected to said magnet and having opposite pole faces spaced apart, an armature positioned .between said pole faces and provided with fixed trunnions adapted to be twisted to permit pivotal movement of said armature, said trunnions being adapted by their resilience to balance the attractive force of said polarizing magnet in all positions of said armature within a working range, means for confining the movement of said armature to said working range, and means for setting up a pulsating magnetic field in said field members thereby to actuate said armature.

5. In an amplifying device, a polarizing magnet, field members formed of magnetizable material connected to the opposite ends of said magnet and having opposed pole faces spaced apart, an armature of magnetizable material mounted for movement between said pole faces, an alternating current input circuit including a magnetizing coil surrounding said armature and arranged to set up a pulsating magnetic field in said eld members to cause said armature to vibrate between said pole faces, a microphone cell arranged to be actuated by the movement of said armature, and coatings applied to said pole faces to confine said armature to a range of movement throughout which the magnetic attraction thereon varies directly with the distance of the armature from the attracting pole face.

6. In amplifying apparatus, a magnetic device having a winding adapted to be connected in an alternating current circuit and having a vibratory part responsive to fluctuations of said current, a contact member movable with said vibratory part, insulating blocks carried by said device on opposite sides of said contact member, tubes mounted in said blocks and projecting therefrom toward said contact member, sleeves of loosely woven cloth fitted over the inner ends of said tubes and engaging opposite faces of said contact member, particles of carbon occupying said tubes and said sleeves and engaging said contact member, and means for adjusting the normal compression of said particles of carbon.

7. In amplifying apparatus, a magnetic device having a winding adapted to be connected in an alternating current circuit and having a vibratory part responsive to fluctuations of said current, a contact member movable with said vibratory part, insulating blocks carried by said device on opposite sides of said contact member, tubes mounted in said blocks and projecting therefrom toward said contact member, sleeves of loosely woven cloth fitted over the inner ends of said tubes and engaging opposite faces of said contact member, particles of granular conducting material occupying said tubes and said sleeves and engaging said contact member, and plugs adjustably engaging the outer ends of said tubes for regulating the normal compression of said particles.

ARTHUR BESSEY SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,748,806 Timmons Feb. 25, 1930 (Other references on following page) Number Bossart Feb. 19, 1929 Number Name Date Eaton Sept. 17, 1935 Pye July 9, 1935 Harrison Apr. 16, 1929 Ringel Aug, 16, 1932 Sundh Dec. 12, 1911 Nettleton Mar. 5, 1929 Faley July 27, 1943 

